1. Field of the Invention
The present invention relates to the field of network interworking and, more particularly, to a method and system for providing mobile voice communication via the Internet and cellular networks.
2. Description of Related Art
Internet telephony, also known as voice over Internet protocol (abbreviated as voice over IP, or simply VoIP), is provided to deliver real time, two-way, synchronous voice traffic over the Internet or corporate Intranets. Furthermore, because of the increasing demand of mobile communication, the VoIP mobility has become an important issue. One of the existing activities in the international standards bodies towards VoIP mobility is the ITU-T Study Group (SG) 16 H.323 Mobile Annex, which addresses mobility issues in layer 2, timers, header compression, the H.323 system architecture, terminal mobility, user mobility and service mobility, so as to provide mobile voice communication over internet.
FIG. 3 shows a typical infrastructure of a hybrid IP/Cellular network and its major components. Assume that a mobile host 321 in a cellular network 32 would like to call a corresponding mobile host 331 in another cellular network 33. Conventionally, the call connection is established by connecting the mobile host 321 to an associated mobile switching center (MSC) 324 via a base station (BS) 322 and a base station controller (BSC) 323, so as to connect to the public switch telephone network (PSTN) 35. The call connection path is further directed to a mobile switching center 334 of the cellular network 33, and thus to the mobile host 331 via a base station controller 333 and a base station 332. Therefore, the call connection path among those networks can be indicated as MSC-PSTN-MSC. Furthermore, the H.323gateway (GW) 311 in the Internet 31 performs signaling conversion, and hence allows the call to be operated across different cellular networks 32 and 33. Under the current version of H.323, the signals are relayed through the PSTN 35 to the H.323 gateway 311. Therefore, the interoperability to cellular networks defined in the current H.323standard can be depicted by the path of MSC-PSTN-GW-PSTN-MSC. This is inefficient because the paths have to go through the circuit-switching PSTN 35, which results in the call occupying too much communication bandwidth. As a result, the communication cost is relatively high.
To solve the aforementioned problem, one would like to direct the paths through the packet-switching Internet 31, instead of the PSTN 35. However, this is not applicable, as the H.323 standard can not satisfy the mobility requirement of the mobile communication. For example, when the mobile host 321 roams from the MSC area controlled by the mobile switching center 324 to another MSC area controlled by a mobile switching center in the cellular network 33, the call connection will be broken, as the H.323 standard does not support the required handoff procedure. Therefore, there is a need for the above mobile voice communication to be improved.